Unit Price Calculator
Bigger is not always cheaper. Enter the price and size of up to three products and this calculator converts everything to a common unit, finds which is genuinely best value, shows how much you save per unit, and tells you the total cost if you buy enough to cover your needs.
Formula
Worked example
Item A: $3.49 for 500 g. Item B: $4.99 for 750 g. Per gram: A = 3.49/500 = $0.00698; B = 4.99/750 = $0.00665. Item B is cheaper by about 4.8% per gram.
Why unit price beats sticker price
The unit price strips away packaging and tells you the cost of one gram, millilitre, sheet or item. A bottle that costs more in total can easily be cheaper per millilitre. A multipack labelled "value size" is not always the best deal. Unit price is the reliable test. Retailers are often required to display it on shelf labels, but they do not always use the same base unit, making side-by-side comparisons unreliable. Doing your own calculation guarantees a fair comparison every time.
Five modes and automatic unit conversion
Choose the mode that matches your product: count (individual items), weight (g, kg, oz, lb), volume (ml, l, fl oz, cup, pint, quart, gallon), or length (mm, cm, m, in, ft, yd). Item A and Item B can use different units within the same mode; for example, one bag in grams and another in ounces. The calculator converts both to a shared base unit (grams for weight, millilitres for volume, metres for length) before dividing, so the comparison is always apples-to-apples.
Compare three items and estimate total spend
Toggle "Compare a third item" to add a third option side by side. This is useful at the supermarket when a store brand, a mid-tier brand and a premium brand are all on the shelf at once. Enable "Estimate total spend" and enter the quantity you need (in base units) to see the total cost for each option at that volume. For example, entering 2000 g shows what you would spend buying enough of each product to get 2 kg in total, making it easy to see the real saving in dollar terms.
When a lower unit price is not the right choice
Unit price assumes you will use every gram or millilitre you buy. If a large pack expires before you finish it, the effective cost per usable unit is much higher. Similarly, if the larger size requires you to change your recipe, buy extra storage or accept lower quality, the apparent saving disappears. Use unit price as the starting point, then apply common sense: perishables, storage limits and personal preference all belong in the final decision.
Common unit conversion reference for shopping
| Mode | You enter | Base unit | Factor |
|---|---|---|---|
| Weight | 1 kg | g | 1 kg = 1,000 g |
| Weight | 1 oz | g | 1 oz = 28.35 g |
| Weight | 1 lb | g | 1 lb = 453.6 g |
| Volume | 1 l | ml | 1 l = 1,000 ml |
| Volume | 1 fl oz | ml | 1 fl oz = 29.57 ml |
| Volume | 1 cup | ml | 1 cup = 236.6 ml |
| Volume | 1 pt | ml | 1 pt = 473.2 ml |
| Volume | 1 gal | ml | 1 gal = 3,785 ml |
| Length | 1 in | m | 1 in = 0.0254 m |
| Length | 1 ft | m | 1 ft = 0.3048 m |
Quick reminder of the conversions used internally. The calculator handles these automatically.
Frequently asked questions
What is unit price and how is it calculated?
Unit price is the cost of one standard unit of a product: one gram, one millilitre, one item, and so on. You calculate it by dividing the total price by the total quantity. For example, a 750 g bottle of shampoo costing $4.99 has a unit price of $4.99 / 750 = $0.00665 per gram. Comparing unit prices across sizes and brands tells you which is genuinely cheaper regardless of packaging.
Can I compare items that use different units, such as grams and ounces?
Yes. Select "Weight" mode, enter Item A in grams and Item B in ounces (or any combination). The calculator converts both to grams before dividing, so the comparison is fair. The same applies to volume: you can mix millilitres, fluid ounces, cups and litres freely.
Is the bigger pack always cheaper per unit?
No. Larger packs often have a lower unit price, but promotions on smaller sizes or premium pricing on club-store sizes can flip that. Multi-item bundles are sometimes priced higher per unit than single items. Always check the unit price rather than assuming the biggest package wins.
How does the total spend estimate work?
Enable "Estimate total spend" and enter the quantity you want to end up with, in the base unit for that mode (grams for weight, millilitres for volume, and so on). The calculator multiplies the unit price by that target quantity to show how much you would spend buying each option. This turns a percentage saving into a concrete dollar figure.
Why does unit price sometimes not give the full picture?
Unit price assumes you will use everything you buy. If a large pack expires or spoils before you finish it, the effective cost per usable unit is higher than the label suggests. Storage space, travel weight and personal preference also matter. Use unit price as your primary filter, then weigh these practical factors before committing.